Thermoplastic elastomer SIS has attracted great attention since its introduction in 1963. It is a triblock copolymer composed of styrene and isoprene.
In the middle is a soft rubber segment isolated from each other, on both sides is a hard plastic segment, at room temperature with the properties of vulcanized rubber, plasticity at high temperatures, and has good elasticity and bond strength, low temperature resistance, good resistance to dissolution , Low solution viscosity, fast curing, etc., so it is usually used to prepare adhesives with SBS or other materials, mainly used as hot melt adhesives and pressure-sensitive adhesives, used in medical, electrical insulation, packaging, protection and masking, logos, Bonding and bonding of composite bags, etc.
However, the SIS has a small polarity, poor oil resistance and solvent resistance, and its application range is greatly limited. For example, there are many disadvantages when it is used as an adhesive at high temperatures or for bonding polar substrates such as shoes and wood. : Adhesion strength with polar materials is not high, heat resistance and weather resistance are poor, especially when used as hot melt pressure sensitive, its softening point is low.
SIS modification principle and method
At present, the research on SIS hot melt pressure-sensitive adhesive modification mainly focuses on three aspects: The first is to modify the SIS elastomer, introduce polar groups or segments on the elastomer, change the polarity of the molecules, including : Epoxidation, graft modification.
The second is the modification of the SIS pressure-sensitive adhesive, which mainly changes the surface tension and polarity of the adhesive by adding other types of binders or additives, thereby improving the adhesion between the adhesive and the adhered material. Second, it is modified by changing the composition of the pressure-sensitive adhesive;
The third is the use of electron beam or ultraviolet light irradiation, the SIS elastomer double bond breaks to generate free radicals, and then perform intramolecular, intermolecular and other polymer polymerization, grafting, cross-linking process .
1, epoxidation modification
Since polystyrene and polyisoprene are non-polar substances, miscibility with polar substances and indirectness of formed adhesives are all limited. The modification of SIS is mainly to introduce a polar Emulsion modified by ESIS, the pressure sensitive adhesive formulated with the best formula and the unmodified SIS pressure sensitive adhesive formulated with the best formula for performance comparison. The results show that ESIS pressure sensitive The peel strength of the adhesive, holding viscosity, aging resistance is better than the unmodified SIS pressure-sensitive adhesive.
2, graft modification
Double bonds exist in the SIS elastomer, which can be used to increase the adhesive's initial viscosity, heat resistance, adhesion, etc. Grafting with SIS and monomer with similar polyolefin structure and surface properties.
Acrylic and acrylic grafts
At present, the domestic research on the graft modification of SIS and acrylic esters is generally carried out by solution grafting method with methyl methacrylate (MMA), butyl methacrylate (BMA), acrylonitrile (AN), acrylic acid ( MAH) modified the monomer for SIS. The experimental results show that MMA and BMA and their mixtures can effectively graft SIS under the action of benzoyl peroxide (BPO), enhance their polarity and flexibility, and improve their polarity. The material shows the adhesive properties.
Butyl rubber modification
Since polyisoprene segments in SIS are easily broken by oxygen, heat, light, and degraded and cross-linked, affecting the performance of pressure-sensitive adhesives, the chemical unsaturation of butyl rubber is low, and polyisobutylene chains are added. Inactive, so that the heat and oxidation resistance of butyl rubber is far superior to other general-purpose rubber.
3, SIS pressure-sensitive adhesive modification
The SIS elastomer itself has no initial tackiness. When it is to be formulated as a pressure-sensitive adhesive, it must be added with a binder resin, softener, anti-aging agent and other additives.
SIS pressure-sensitive adhesive modification, there are two main ways of modification, one is to change the composition or content of pressure-sensitive adhesive, according to the adhesive requirements to select different tackifying resins, solvents and their additives or the content of each component The second is the modification of blends. The polarity of the system is increased by the addition of other types of adhesives or additives to increase the adhesion of the mixed binder to the polar fabric, which is currently used to produce special properties. Mixture often used method.
SIS pressure-sensitive adhesive modification can significantly improve the adhesion with polar materials, and the heat resistance and weather resistance must also be improved. This modification is relatively simple, the required equipment is relatively simple, compared with the modification of elastomers, raw materials With low energy consumption, it is suitable for the company to produce adhesives that meet different performance requirements.
4, UV or electron beam modification
Ultraviolet light or electron beam modification is that after the hot melt pressure sensitive adhesive is coated, a short electron beam or ultraviolet irradiation breaks the double bonds of the SIS elastomer to generate free radicals, and then the polymerization reaction is performed.
Generally, after coating, the elastomer is cooled to below the Tg of the SIS segment. If the SIS is only physically cross-linked, electron beam or ultraviolet radiation is used, and then some chemical cross-linking is performed, which can make up for the lack of physical cross-linking. Can greatly improve the temperature resistance and solvent resistance of the adhesive without affecting the viscosity.
UV and electron beam modification can improve peel strength and stickiness. It is suitable for application in some special fields. It has a small environmental pollution and very little raw materials and energy consumption. It is a promising technology.